As a developer well-versed in HTML, HTML5, JavaScript, and specifically React Native - one of the most popular frameworks for mobile app development, I have the perfect skill-set you need for your project. My experience extends to adding new features to existing applications, therefore I can seamlessly dive right into your ongoing project. I am comfortable with quick turnarounds and fast-paced work, something that will be invaluable given your urgent hiring need.
Moreover, my understanding of React Native principles and proficiency in Javascript align closely with your project's requirements. Being a quick learner is second nature to me, thus even if the specifics of the task are yet to be disclosed, rest assured that I will understand and take on any project mid-development without hiccups.
Additionally, my knowledge isn’t confined solely to React Native; I bring multifaceted skills including front-end and back-end development. So, not only can I add the new features required but also assist in analyzing its impact on other components of your system. With me on board, you won't just get a proficient React Native developer but a proactive problem solver. Let's leap into this challenge together!